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Acceptor Strength (acceptor + strength)
Selected AbstractsSyntheses of New 3,6-Carbazole-Based Donor/Acceptor Conjugated Copolymers for Optoelectronic Device ApplicationsMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 18 2010Mei-Hsiu Lai Abstract The syntheses, properties, and optoelectronic device characteristics of four new 3,6-carbazole-based donor/acceptor conjugated copolymers are reported. Such copolymers are used to explore the effects of acceptor strength and backbone coplanarity on the electronic and optoelectronic properties. The optical bandgaps of the studied copolymers are PCzQ (2.29,eV),>,PCzDTQ (1.91,eV),>,PCzTP (1.75,eV),>,PCzDTTP (1.49,eV), which are much smaller than the parent poly(3,6-carbazole). The power conversion efficiency of the photovoltaic cells fabricated from blends of copolymer/PC61BM or PC71BM reached 1.01 and 1.73% by varying the film thickness or blend ratio. The experimental results suggest the potential application of 3,6-carbazole acceptor conjugated copolymers in optoelectronic devices. [source] Nitroxide spin probe study of probe size, hydrogen bonding and polymer matrix rigidity effects on poly(acrylic acid)/poly(ethylene oxide) complexesMAGNETIC RESONANCE IN CHEMISTRY, Issue 7 2003Li Tan Abstract An electron spin resonance (ESR) spin probe study was performed on 1 : 1 by weight poly(acrylic acid) (PAA)/poly(ethylene oxide) (PEO) complex over the 100,450 K temperature range with a series of tetramethylpiperidyloxy-based spin probes. Measurements of the parameters T5mT, Ta and Td demonstrated the effects of probe size and the strength of hydrogen bonding. The probes in the series Tempone, Tempo, Tempol and Tamine (respectively 4-oxo-, unsubstituted, 4-hydroxy- and 4-amino-2,2,6,6,-tetramethylpiperidine -1-oxyl) displayed noticeable increases in the hydrogen-bonding effect, as indicated by Ta and Td. These increases correlated with increasing hydrogen bond acceptor strength. On the other hand, as the probe size became larger, T5mT gradually increased due to the free volume decrease. These effects were analyzed using the established theoretical relationship of T5mT to probe volume expressed by f. Meanwhile, in order to investigate the effect of polymer matrix rigidity, a similar study was performed with a nitroxide spin probe, 2,2,6,6-tetramethyl-1-piperidine-1-oxyl (Tempo), on PAA/PEO complexes of different weight compositions. The quantitative fast motion fraction in the composite ESR spectrum was calculated. The influence of changes in the composition of PAA on the molecular mobility was characterized by changes of the spectral parameters and ,c. The molecular mobility was shown to diminish with increasing content of PAA in PAA/PEO blends duo to the restriction of the polymer matrix rigidity increase. Copyright © 2003 John Wiley & Sons, Ltd. [source] Transition-Metal Complexes [(PMe3)2Cl2M(E)] and [(PMe3)2(CO)2M(E)] with Naked Group,14 Atoms (E=C,Sn) as Ligands; Part 2: Complexation with W(CO)5CHEMISTRY - A EUROPEAN JOURNAL, Issue 35 2009Pattiyil Parameswaran Dr. Abstract Density functional calculations at the BP86/TZ2P level were carried out to understand the ligand properties of the 16-valence-electron(VE) Group,14 complexes [(PMe3)2Cl2M(E)] (1ME) and the 18-VE Group,14 complexes [(PMe3)2(CO)2M(E)] (2ME; M=Fe, Ru, Os; E=C, Si, Ge, Sn) in complexation with W(CO)5. Calculations were also carried out for the complexes (CO)5W,EO. The complexes [(PMe3)2Cl2M(E)] and [(PMe3)2(CO)2M(E)] bind strongly to W(CO)5 yielding the adducts 1ME,W(CO)5 and 2ME,W(CO)5, which have C2v equilibrium geometries. The bond strengths of the heavier Group,14 ligands 1ME (E=Si,Sn) are uniformly larger, by about 6,7,kcal,mol,1, than those of the respective EO ligand in (CO)5W-EO, while the carbon complexes 1MC,W(CO)5 have comparable bond dissociation energies (BDE) to CO. The heavier 18-VE ligands 2ME (E=Si,Sn) are about 23,25,kcal,mol,1 more strongly bonded than the associated EO ligand, while the BDE of 2MC is about 17,21,kcal,mol,1 larger than that of CO. Analysis of the bonding with an energy-decomposition scheme reveals that 1ME is isolobal with EO and that the nature of the bonding in 1ME,W(CO)5 is very similar to that in (CO)5W,EO. The ligands 1ME are slightly weaker , acceptors than EO while the ,-acceptor strength of 2ME is even lower. [source] The Diversity of Difluoroacetylene Coordination Modes Obtained by Coupling Fluorocarbyne Ligands on Binuclear Manganese Carbonyl SitesCHEMISTRY - A EUROPEAN JOURNAL, Issue 22 2009Xian-mei Liu Abstract One Mn or two? The fluorocarbyne manganese carbonyl complexes [Mn(CF)(CO)n] (n=3,,4) and [Mn2(CF)2(CO)n] (n=4,7; see picture) have been investigated by density functional theory. In mononuclear complexes the CF ligand behaves very much like the NO ligand in terms of ,-acceptor strength. In binuclear complexes the two CF ligands couple in many of the low-energy structures to form a bridging C2F2 ligand derived from difluoroacetylene. Recent work has shown that the fluorocarbyne ligand CF, isoelectronic with the NO ligand, can be generated by the defluorination of CF3 metal complexes, as illustrated by the 2006 synthesis by Hughes et,al. of [C5H5Mo(CF)(CO)2] in good yield by the defluorination of [C5H5Mo(CF3)(CO)3]. The fluorocarbyne ligand has now been investigated as a ligand in the manganese carbonyl complexes [Mn(CF)(CO)n] (n=3,,4) and [Mn2(CF)2(CO)n] (n=4,7) by using density functional theory. In mononuclear complexes, such as [Mn(CF)(CO)4], the CF ligand behaves very much like the NO ligand in terms of ,-acceptor strength. However, in the binuclear complexes the two CF ligands couple in many of the low-energy structures to form a bridging C2F2 ligand derived, at least formally, from difluoroacetylene, FCCF. The geometries of such [Mn2(C2F2)(CO)n] complexes suggest several different bonding modes of the bridging C2F2 unit. These include bonding through the orthogonal ,,bonds of FCCF, similar to the well-known [R2C2Co2(CO)6] complexes, or bonding of the C2F2 unit as a symmetrical or unsymmetrical biscarbene. This research suggests that fluorocarbyne metal chemistry can serve as a means for obtaining a variety of difluoroacetylene metal complexes, thereby avoiding the need for synthesizing and handling the very unstable difluoroacetylene. [source] Variable-Temperature Powder X-ray Diffraction of Aromatic Carboxylic Acid and Carboxamide CocrystalsCHEMISTRY - AN ASIAN JOURNAL, Issue 4 2007L. Sreenivas Reddy Abstract The effect of temperature on the cocrystallization of benzoic acid (BA), pentafluorobenzoic acid (FBA), benzamide (BAm), and pentafluorobenzamide (FBAm) is examined in the solid state. BA and FBA formed a 1:1 complex 1 at ambient temperature by grinding with a mortar and pestle. Grinding FBA and BAm together resulted in partial conversion into the 1:1 adduct 2 at 28,°C and complete transformation into the product cocrystal at 78,°C. Further heating (80,100,°C) and then cooling to room temperature gave a different powder pattern from that of 2. BAm and FBAm hardly reacted at ambient temperature, but they afforded the 1:1 cocrystal 3 by melt cocrystallization at 110,115,°C. Both BA+FBAm (4) and BA+BAm (5) reacted to give new crystalline phases upon heating, but the structures of these products could not be determined owing to a lack of diffraction-quality single crystals. The stronger COOH and CONH2 hydrogen-bonding groups of FBA and FBAm yielded the equimolar cocrystal 6 at room temperature, and heating of these solids to 90,100,°C gave a new crystalline phase. The X-ray crystal structures of 1, 2, 3, and 6 are sustained by the acid,acid/amide,amide homosynthons or acid,amide heterosynthon, with additional stabilization from phenyl,perfluorophenyl stacking in 1 and 3. The temperature required for complete transformation into the cocrystal was monitored by in,situ variable-temperature powder X-ray diffraction (VT-PXRD), and formation of the cocrystal was confirmed by matching the experimental peak profile with the simulated diffraction pattern. The reactivity of H-bonding groups and the temperature for cocrystallization are in good agreement with the donor and acceptor strengths of the COOH and CONH2 groups. It was necessary to determine the exact temperature range for quantitative cocrystallization in each case because excessive heating caused undesirable phase transitions. [source] | ||||||||||